Merge `InitModifier` and `UpdateModifier` (#292) #566

Job	Run time
Check format	1m 13s
Coverage	4m 38s
run-examples	12m 53s
build (2d, stable, windows-latest)	8m 13s
build (2d, stable, ubuntu-latest)	12m 42s
build (2d, stable, macos-latest)	9m 12s
build (3d, stable, windows-latest)	8m 13s
build (3d, stable, ubuntu-latest)	13m 2s
build (3d, stable, macos-latest)	3m 20s
build (all, stable, windows-latest)	8m 0s
build (all, stable, ubuntu-latest)	7m 35s
build (all, stable, macos-latest)	3m 18s
	1h 32m 19s

Provide feedback